1. Field of the Invention
The present invention relates to a plasma display device.
2. Description of the Related Art
In conventional plasma display devices, power MOSFET (Metal-Oxide Semiconductor Field Effect Transistor) has been a most general output element for their sustain circuits. In contrast to this, some of recent sustain circuits of the plasma display devices phase into use of IGBT (Insulated Gate Bipolar Transistor) having both of input characteristic, which is an advantage of power MOSFET, and low-saturation voltage characteristic, which is an advantage of bipolar transistor, with a shortened turn-off time (for example, see Patent Document. 1 (Japanese Patent Application Laid-Open No. 2000-330514)).
Another proposal is made on an IGBT-incorporated driver IC for driving the plasma displays in which a power MOSFET and an IGBT are connected in a form of totem pole connection (for example, see Patent Document 2 (Japanese Patent Application Laid-Open No. Hei 8-4605.3)).
The IGBT, characterized by its conductivity modification effect just like bipolar transistors, can lower the saturation voltage under current supply. The IGBT can thus realize a basic operation as an output device of the sustain circuit of the plasma display devices through reduction in the turn-off time. The IGBTs currently commercialized are certainly reduced in the turn-off time as compared with the conventional ones, but are still inferior to the power MOSFET because they are longer both in the turn-on time and turn-off time, and are thus disadvantageous in the switching loss.
In consideration of the above situation, a proposal has been made on an inverter for air conditioners, which comprises a power MOSFET which is brought into a conduction state when applied with a first drive voltage, and an IGBT which is brought into a conduction state when applied with a second drive voltage having a different level from that of the first drive voltage, where the power MOSFET and the IGBT are connected in parallel with respect to current supplied to a load (for example, see Patent Document 3 (Japanese Patent Application Laid-Open No. 2002-16486)). In the above-described inverter for air conditioners, the first drive voltage, which drives the power MOSFET only, is applied to the gate electrode when the current to be supplied to the load is relatively small, whereas the second drive voltage, which drives mainly the IGBT and is larger than the first drive voltage is applied to the gate electrode when the current to be supplied to the load is relatively large.
In the technology disclosed in the Patent Document 3, both of the power. MOSFET and IGBT are driven during a large-current driving (start-up) of the inverter for air conditioners or the like. Whereas during a small-current driving (stationary driving) of the inverter for air conditioners or the like, the IGBT is turned off, and only the power MOSFET is driven so as to reduce the power loss during the stationary driving.
The circuit disclosed in the Patent Document 3 applied to the plasma display devices operates during the stationary driving so as to turn off the IGBT and activate only the power MOSFET, so that it can ensure only a small drive margin as being affected by voltage fluctuation due to discharge current. This may consequently result in degradation in the display characteristics which is typified by generation of noise or flicker. In particular the plasma display devices having a screen size of typically 42 inches or larger tend to suffer from a large voltage fluctuation ascribable to the discharge current, and are highly causative of degradation in the display characteristics.